The Radeon GPUs are capped at 6 signals, regardless of how many are actually connected to it (through MST hubs, splitters, etc.) Because of that, you can have 9 monitors connected to that single card with the MST hub, but Catalyst and Windows will only let you have 6 enabled at one time. The other three will be recognized, but cannot be enabled without disabling one of the other monitors first. Sadly, it's a limitation of the GPU itself, where 6 active signals per GPU is the maximum.
On the "unsupported configuration" side, there are HDMI splitters that take one HDMI signal and split it to two monitors. This only clones the original signal, it's definitely not supported by AMD, and the splitters tend to be incredibly finicky and tempermental, but it could work if you intend to duplicate monitors. It definitely wouldn't allow Eyefinity over 9 monitors though.
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